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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

58

CALCIUM CARBIDE

volume is made up to the mark with distilled water and, after mixing,
50 or 100 c.c. are titrated with N-alkali in presence of phenolphthalein.
i c.c. of N-alkali = 0-07907 gram of anhydrous calcium acetate = 0-06003
gram of acetic acid.

It is well to ascertain that the distillate does not contain appreciable
quantities of hydrochloric acid derived from chlorides in the acetate (silver
nitrate should give at most a faint opalescence). The small amounts of
propionic and butyric acids, etc., are practically negligible.

*

* *

Crude calcium acetate (pyrolignite) usually contains 70-80% of true anhy-
drous acetate and hence 53-60% of acetic acid. The pure calcium acetate used
in dyeing is mostly prepared by the consumer himself by dissolving lime or cal-
cium carbonate in acetic acid ; it should partieiilarly be free from iron.

CALCIUM   CARBIDE
OaC2 -.- 64

'Fused masses with crystalline fracture, grayish-brown, in colour and
alterable in moist air. With water it decomposes, giving acetylene and
calcium hydroxide. It may contain, as impurities, calcium sulphide and
phosphide, ammonium sulphide, silica,, ferrosilicoti and silicon carbide,
its value depending essentially on its yield of acetylene. The product
being always non-homogeneous, special, care attaches to sampling.

1.  Sampling.- ....... According  to  the  number  of  casks   (drums)   in   the

parcel to be analysed, a sample of at least. '2, kilos is taken from. a. cask (for
lots up to 20 drums) or from 5% or 10% of the casks (for lots of more than
20 drums).    Before* being opened the ca.sk is inverted twice to distribute
the sma.ll pieces and dust as uniformly as possible throughout the coarse.
The sample is placed immediately in glass vessels with ground stoppers or
in metal vessels with soldered lids.1

2.  Various Impurities.   As a rule the carbide itself is not investi-
gated, it being sufficient to determine (lie yield of acetylene and. to test:
the purity of the gas (sc-c- below).    Where necessary, however, the carbide
may be treated with a, sugar. solution in which the lime remains dissolved,
wliereas the impurities remain undissolved and may be recognised by the
ordinary analytical methods,    As a. rule these impurities represent 3- (>%
of the carbide.

3.  Yield of Acetylene,-   This is determined by treating a known weight
of the carbide with water (or, better, brine) and measuring I he volume of
gas evolved.    Various forms of gasometer or apparatus may be used to
collect, and measure1 the gas.2

The determination may be ina.de in one of two methods ; Total gasifica-
tion, which consists in decomposing with water (in one or more lots) the,
whole of tlie sample as it, is taken, and ]\trl.hd ^tisi/ictilinn, which consists

1  See idwAcctyknc, by V. B. Lowes (New York, t<)<><»). JHst, (•hcni.-ti't'Im, Analyse.

2  Sec works cited in proecdinK note, and also artieU'.s by Fonwnti in IM chimwa
industrial, 1902, Vol. VI, p. 182 ; Reeehi in (iuzs. c/iim, Hal., !•)<».!, 1, p. i <>;•{ ; Maguuniixi
and Vunru'ni, ibid., 1900, I, p. 401.d vessels.of ethyl acetate in 100 c.c. of the amyl acetate